Warm Up · Reverse Integer

Reverse Digits of an Integer

Problem Statement

Write a function reverse(x) that takes a 32-bit signed integer and returns its digits reversed. If the reversed value overflows the 32-bit signed integer range, return 0.

Requirements

Reverse the digits of a 32-bit signed integer.
Return 0 if the result overflows.

Examples

Input: 123→Output: 321

Input: -123→Output: -321

Input: 1534236469→Output: 0 (overflow)

Approach

Preserve the Original: Save x in xCopy.
Work with Absolute Value: Use Math.abs(x) or abs(x) to simplify reversal.
Reverse Digits: Initialize rev = 0. While x != 0: last = x % 10, rev = rev * 10 + last, x //= 10.
Check for Overflow: Return 0 if the reversed number is outside the 32-bit int range.
Restore Sign: Return -rev if xCopy < 0, else rev.

Time & Space Complexity

Time Complexity: O(d) - where d is the number of digits.

Space Complexity: O(1) - constant space.

Visualisation

1Start with the numberx = 123

2Take the last digit, push it onto revrev = 3 → 32 → 321

3Check the 32-bit limitrev > 2**31 - 1 → 0

4Restore the sign321

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